Below you will see an image with shadows in it. (This is a Java image and may take up to a minute to load.) The image shows a square card on a shelf with a wall behind it.
There are colored lights just this side of the shelf that cast huge shadows on
the wall.

The two circles at the bottom are the lights. Drag to move
them and click on the circles to change their colors.

The square in the middle casts a shadow. Drag to move it.

See if you can figure out the following. If you want some hints read the background information. (You will get to write about what you figure out on the next page.)